High resolution two‐dimensional polyacrylamide gel electrophoresis has been used to detect a soluble protein in extracts of human kidney which was not present in the electrophoretograms of other human tissues. This protein, coded kidney‐acidic protein‐60 (KAP‐60) was purified to homogeneity and was characterized as having a native molecular weight of 85000, a monomer molecular weight of 35 000 and an isoelectric point of 5.6. KAP‐60 was devoid of detectable carbohydrate or phosphate groups. Injection of the protein into rabbits produced antisera which were used to develop a radioimmunoassay for the protein and to localize the protein to specific cells within the kidney by the immunoperoxidase technique. A survey of human tissues by radioimmunoassay showed that KAP‐60 was present in human kidney at approximately 150 times the concentration found in human liver and 300 times the level found in other human organs examined. Immunohistochemistry localized the protein to the proximal and collecting tubules in the kidney with no staining of glomeruli or distal tubules. The present study illustrates the use of high‐resolution two‐dimensional electrophoretic techniques in the detection of human tissue‐specific proteins which may prove of clinical value in the biochemical diagnosis of tissue‐specific damage.